The active component of RELENZA is zanamivir. The chemical name of zanamivir is 5-(acetylamino)-4-[(aminoiminomethyl)-amino]-2,6-anhydro-3,4,5-trideoxy-D-glycero-D-galacto-non-2-enonic acid. It has a molecular formula of C₁₂H₂₀N₄O₇ and a molecular weight of 332.3. It has the following structural formula:

Zanamivir is a white to off-white powder with a solubility of approximately 18 mg/mL in water at 20°C.

RELENZA is for administration to the respiratory tract by oral inhalation only. Each RELENZA ROTADISK® contains 4 regularly spaced double-foil blisters with each blister containing a powder mixture of 5 mg of zanamivir and 20 mg of lactose (which contains milk proteins). The contents of each blister are inhaled using a specially designed breath-activated plastic device for inhaling powder called the DISKHALER. After a RELENZA ROTADISK is loaded into the DISKHALER, a blister that contains medication is pierced and the zanamivir is dispersed into the air stream created when the patient inhales through the mouthpiece. The amount of drug delivered to the respiratory tract will depend on patient factors such as inspiratory flow. Under standardized in vitro testing, RELENZA ROTADISK delivers 4 mg of zanamivir from the DISKHALER device when tested at a pressure drop of 3 kPa (corresponding to a flow rate of about 62 to 65 L/min) for 3 seconds. In a study of 5 adult and 5 adolescent patients with obstructive airway diseases, the combined peak inspiratory flow rates (PIFR) ranged from 66 to 140 L/min. In a separate study of 16 pediatric patients, PIFR results were more variable; 4 did not achieve measurable flow rates, and PIFR for measurable inhalations by 12 children ranged from 30.5 to 122.4 L/min. Only 1 of 4 children under age 8 had a measurable flow rate (see CLINICAL PHARMACOLOGY: Pediatric Patients, INDICATIONS AND USAGE: Description of Clinical Studies, and PRECAUTIONS: Pediatric Use).

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